A wireless metropolitan area network (WMAN) offers broadband network access to subscribers in a metropolitan area where exterior antennas in the metropolitan area provide access to the broadband network (also termed a core network). A WMAN allows a subscriber of the WMAN to freely move while remaining connected to the core network. The subscriber connects to the core network by associating with access points (APs) of the WMAN. An AP is also known as a base station. As such, the AP provides wireless coverage for a specific area so that subscribers within coverage are connected to the core network. A subscriber may be connected to the core network through a network of APs (also termed “backhaul”).
As the subscriber moves between APs of the WMAN, the connection to a first AP may by dropped as needed, and a connection to a target AP may be established. The process of transferring the subscriber's connection from one AP to another AP is known as hand-off. For example, when the subscriber is in the coverage area of a first AP, the subscriber is connected to the core network via the first AP. However, when the subscriber moves out of the coverage area of the first AP, the subscriber loses its associated with the first AP and it becomes associated with another AP, namely a second AP.
A subscriber may lose its association with an AP more quickly when the subscriber is moving at high speeds. As such, had-off becomes more complicated when the time it takes to hand-off is larger than the time spent by the subscriber within a specific AP coverage area. For example, when a subscriber moves at 70 MPH or more, the subscriber may move between APs in a few seconds. If the association set up takes a very lone time, even as short as 500 ms, packets may be lost in the transition and maintaining a reasonable quality of service (QoS) is challenging. Even if the subscriber is not moving at high speeds, many times in a WMAN a subscriber may lose connection with a specific AP without prior warning. For example, if the subscriber is in a WMAN with high rise buildings where antennas are placed at low sites, a subscriber turning the corner may lose connection with its previously associated AP without any prior warning thereby causing packets to be lost and potentially disrupting the flow of packets to the subscriber.
Moreover, many existing hand-off solutions are not applicable to a mission critical situation where at an incident scene a subscriber may lose its connectivity to an AP (e.g. due to power discrepancies and/or APs coming in and out of service). Additionally, current hand-off solutions do not address the situation where a subscriber hands-off to an AP that can not serve the subscriber, for example because the AP is heavily loaded. Further, existing hand-off solutions do not address the problem where an AP providing connectivity to the core network in a multiple layered AP backhaul fails, then the APs that are served by the failed AP need to fine another AP for connecting to the core network. In such a situation, these APs are performing hand-off in order to prevent the loss of packets that are with the failed AP. Further yet, current hand-off solutions do not provided the ability to provided secure links since secure links take time to set up.
Thus, there is a need for a new method and a system for facilitating fast handoff in a Wireless Metropolitan Area Network (WMAN).